Systems and methods for low latency copy operations in non-volatile memory

ABSTRACT

Techniques and systems are provided for copying, with or without error-fixing or corrections, data associated with a first set of locations to a second set of locations in a flash memory. Example methods disclosed, when performed by a flash memory controller, can significantly improve latency of operations. Embodiments of the disclosure can be used, for example, in a garbage collection process of a NAND flash memory.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a non-provisional application and claims the benefitand priority of U.S. Provisional Application No. 62/251,519, filed onNov. 5, 2015, titled “EFFICIENT GARBAGE COLLECTION USING COPY BACKCOMMANDS,” which is herein incorporated by reference in its entirety forall purposes.

FIELD

The present invention relates generally to systems, methods andapparatus for storage devices, and specifically to improving performanceof non-volatile memory devices.

BACKGROUND

Non-volatile memory devices such as Solid State Drives (SSDs) arefinding new applications in consumer electronics. For example, they arereplacing Hard Disk Drives (HDDs), which typically comprise rapidlyrotating disks (platters). Non-volatile memories, sometimes referred toas ‘flash memories’ or ‘flash memory devices’ (for example, NAND and NORflash memory devices), are used in media storage, cameras, mobilephones, mobile computers, laptop computers, USB flash drives, etc.Non-volatile memory provides a relatively reliable, compact,cost-effective, and easily accessible method of storing data when thepower is off.

Several operations can require data from a first set of locations to becopied to a second set of locations within a flash memory device. Oneexample of such an operation is the recycling of blocks during the‘garbage collection’ process. Garbage collection is deployed in manystorage systems, such as solid-state disk drives, where there arephysical limitations on in-place data update. As part of the garbagecollection process in a NAND flash memory device, data from a ‘victim’block is copied—either as is, or with corrections—to a ‘target’ block inthe flash memory device so that the victim block can be erased and madeavailable.

SUMMARY

Embodiments of the invention pertain to systems, methods, andcomputer-readable instructions for copying and/or moving data from onelocation to another in a flash memory. ‘Moving’ or ‘copying’ as used inthis description can include both copying as-is and/or copying withchanges or corrections. Moving or copying can also broadly refer toscenarios where the original source data is maintained, and/or scenarioswhere the original source data is subsequently erased.

According to some embodiments, a method for moving data in the flashmemory can comprise reading, by a flash memory controller, dataassociated with a first set of locations from the flash memory. Inexamples, the data associated with the first set of locations can becopied from the flash memory to a flash buffer and then read into theflash memory controller. The method can further comprise estimating, atthe flash memory controller, at least one error location in the dataassociated with the first set of locations. Information identifying theat least one error location can be sent from the flash memory controllerfor error-fixing. The error-fixing can operate on a copy of the dataassociated with the first set of locations to result in corrected dataassociated with the first set of locations. In examples, the copy of thedata associated with the first set of locations can be present in theflash buffer.

The method can further comprise issuing, from the flash memorycontroller, a command that causes the corrected data associated with thefirst set of locations to be stored in a second set of locations of theflash memory, the second set of locations different from the first setof locations. In examples, the command that causes the corrected dataassociated with the first set of locations to be stored in a second setof locations can comprise a copy back command. In examples, the commandcan be a modified version of a copy back command.

In some embodiments, the moving data in the flash memory can occur aspart of a garbage collection process in a NAND flash memory device.

In some embodiments, estimating the at least one error location in thedata associated with the first set of locations can comprise applying anError Correction Code (ECC) algorithm to the data associated with thefirst set of locations. In examples, this estimation can occur at theflash memory controller.

In some embodiments, the first set of locations and the second set oflocations can be on the same plane of the flash memory. In otherembodiments, the first set of locations can be on a first plane of theflash memory, whereas the second set of locations can be on a secondplane of the flash memory. In such embodiments, the second plane can bedifferent from the first plane but on the same die. In some embodiments,the first set of locations and the second set of locations can be ondifferent dies of the flash memory.

In some embodiments, the sending the information identifying the atleast one error location can be based on a condition being satisfied.The condition being satisfied can be based on a count of locations witherrors in the first set of locations. More particularly, in examples,the condition being satisfied can be based on the count of locationswith errors in the first set of locations being higher than a thresholdnumber of locations. In other examples, the condition being satisfiedcan be based on the percentage of locations with errors in the first setof locations exceeding a threshold percentage.

In some embodiments, the error-fixing can comprise a binary flip of abit at the one error location in the copy of the data associated withthe first set of locations. In some embodiments, the error-fixing occursat a flash buffer coupled to the flash memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a system including a host, acontroller, and a non-volatile memory according to embodiments;

FIG. 2 is a simplified illustration of the organization of an examplenon-volatile memory die, according to embodiments;

FIG. 3A, FIG. 3B, and FIG. 3C illustrate three examples of a victimblock and a target block, according to embodiments;

FIG. 4 is a simplified block diagram illustrating a flash memory deviceaccording to some embodiments;

FIG. 5 is a flowchart illustrating a method of moving data in a flashmemory according to embodiments;

FIG. 6 is a flowchart illustrating another method of moving data in aflash memory according to embodiments;

FIG. 7 is a flowchart illustrating another method of moving data in aflash memory according to embodiments; and

FIG. 8 is a simplified illustration of a computer device comprising anembodiment.

DETAILED DESCRIPTION

Certain aspects and embodiments of this disclosure are provided below.Some of these aspects and embodiments may be applied independently andsome of them may be applied in combination as would be apparent to thoseof skill in the art. In the following description, for the purposes ofexplanation, specific details are set forth in order to provide athorough understanding of embodiments. However, it will be apparent thatvarious embodiments may be practiced without these specific details. Thefigures and description are not intended to be restrictive.

The ensuing description provides examples, and is not intended to limitthe scope, applicability, or configuration of the disclosure. Rather,the ensuing description of the exemplary embodiments will provide thoseskilled in the art with an enabling description for implementing anexemplary embodiment. It should be understood that various changes maybe made in the function and arrangement of elements without departingfrom the spirit and scope of the invention as set forth in the appendedclaims.

Specific details are given in the following description to provide athorough understanding of the embodiments. However, it will beunderstood by one of ordinary skill in the art that the embodiments maybe practiced without these specific details. For example, circuits,systems, networks, processes, and other components may be shown ascomponents in block diagram form in order not to obscure the embodimentsin unnecessary detail. In other instances, well-known circuits,processes, algorithms, structures, and techniques may be shown withoutunnecessary detail in order to avoid obscuring the embodiments.

Also, it is noted that individual embodiments may be described as aprocess which is depicted as a flowchart, a flow diagram, a data flowdiagram, a structure diagram, or a block diagram. Although a flowchartmay describe the operations as a sequential process, many of theoperations can be performed in parallel or concurrently. In addition,the order of the operations may be re-arranged. A process is terminatedwhen its operations are completed, but could have additional steps notincluded in a figure. A process may correspond to a method, a function,a procedure, a subroutine, a subprogram, etc. When a process correspondsto a function, its termination can correspond to a return of thefunction to the calling function or the main function.

The term “computer-readable medium” includes, but is not limited to,portable or non-portable storage devices, optical storage devices, andvarious other mediums capable of storing, containing, or carryinginstruction(s) and/or data. A computer-readable medium may include anon-transitory medium in which data can be stored and that does notinclude carrier waves and/or transitory electronic signals propagatingwirelessly or over wired connections. Examples of a non-transitorymedium may include, but are not limited to, a magnetic disk or tape,optical storage media such as compact disk (CD) or digital versatiledisk (DVD), flash memory, memory or memory devices. A computer-readablemedium may have stored thereon code and/or machine-executableinstructions that may represent a procedure, a function, a subprogram, aprogram, a routine, a subroutine, a module, a software package, a class,or any combination of instructions, data structures, or programstatements. A code segment may be coupled to another code segment or ahardware circuit by passing and/or receiving information, data,arguments, parameters, or memory contents. Information, arguments,parameters, data, etc. may be passed, forwarded, or transmitted via anysuitable means including memory sharing, message passing, token passing,network transmission, or the like.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middlewareor microcode, the program code or code segments to perform the necessarytasks (e.g., a computer-program product) may be stored in acomputer-readable or machine-readable medium. A processor(s) may performthe necessary tasks.

The following detailed description together with the accompanyingdrawings in which the same reference numerals are sometimes used inmultiple figures to designate similar or identical structures structuralelements, provide a better understanding of the nature and advantages ofthe present invention.

Embodiments of the invention pertain to systems, methods, andcomputer-readable instructions for copying and/or moving data from onelocation to another in a flash memory. For example, embodiments can beused in ‘garbage collection’ process. More specifically, methods,systems, and computer-readable media as described in the disclosure canbe used, for example, to recycle blocks in a NAND flash memory device.

More generally, methods, systems, and computer-readable media asdescribed in the disclosure can be used to copy data from a first set oflocations to a second set of locations in a flash memory. According tosome embodiments, such copying can also including error-fixing.

Several processes in flash memory devices can introduce latency andaffect the speed and performance of the device from a user perspective.Of these processes, some can involve copying data from one set oflocations to another because of limitations in in-place updating of datain some flash memory devices. For example, processes such as garbagecollection, data cycling from read disturb and retention losses canrequire data to be copied. Copying data from one location to another canintroduce significant latency, thereby negatively impacting userexperience.

Data associated with or present in the first set of locations (whichneeds to be copied) can have errors from various sources. Before data iscopied from one location to another, errors in the data may need to becorrected to avoid propagation as the data is moved from one location toanother. Error correction algorithms are capable of correcting theseerrors to some extent; however, if the number of errors in the data islarge, error correction may not be able to fix all errors. The processof copying data from the first set of locations to the second set oflocations can introduce further errors.

Embodiments of solutions presented can involve various methods ofcorrecting errors in the data associated with the first set of locationsbefore being copied to a second set of locations. In examples, upondetermining error locations in the data associated with the first set oflocations by the ECC decoder of the flash memory controller, the flashmemory controller can send information identifying these errorlocations. The error locations can be used, for example by the flashmemory, for error fixing to generate corrected data associated with thefirst set of locations. Examples will be provided with reference toFIGS. 6 and 7. Sending error locations in the first set of locationsinstead of encoding and sending all the data associated with the firstset of locations can significantly reduce latency as described below. Insome embodiments, latency can be reduced by determining that errors inthe first set of locations need not be corrected during the copy, andare better left to be corrected by ECC later. Examples will be providedwith reference to FIG. 5.

FIG. 1 describes the general high level architecture of a systemcomprising a host, a flash memory controller, and a flash memory. FIG. 2describes an examples of the structure of a flash memory. FIG. 3A, FIG.3B, and FIG. 3C illustrate three examples of a victim block and a targetblock. FIG. 4 is a simplified block diagram illustrating a flash memorydevice according to some embodiments. FIG. 5-7 are flowchartsillustrating methods of moving data in a flash memory according toembodiments. FIG. 8 is a simplified illustration of a computer devicecomprising an embodiment.

FIG. 1 is a simplified block diagram illustrating a system 100 includinga host 110, a flash memory controller 120, and a flash memory 130,according to embodiments. In some implementations, flash memory 130 canbe a NAND flash. In other implementations, non-volatile memory 130 canbe a NOR flash memory configured to interact externally as a NAND flash.Flash memory 130 can be designed to store data in the absence of acontinuous or substantially continuous external power supply. In someexamples, flash memory 130 can be used for secondary data storage, forexample, in a computer system such as a laptop. In such examples, aflash memory device 140 can replace a magnetic hard disk drive (HDD). Insome examples, flash memory controller 120 can be external to flashmemory device 140. In some such examples, flash memory controller 120can interact with a plurality of flash memories. The architecture andorganization of one example flash memory will be provided later in thespecification. In some embodiments, other non-volatile memory can beused in place of or in addition to flash memory 130. Examples caninclude read only memory (ROM), a mask ROM (MROM), a programmable ROM(PROM), an erasable programmable ROM (EPROM), an electrically erasableprogrammable ROM (EEPROM), Ferroelectric RAM (F-RAM), MagnetoresistiveRAM (RAM), polymer-based organic memory, holographic memory, phasechange memory and the like.

Host 110 can include any appropriate hardware device, softwareapplication, or a combination of hardware and software. In someembodiments, host 110 can include a host-side controller (not shown). Inembodiments, controller 120 can interface between host 110 andnon-volatile memory 130. Controller 120 can be configured to receivevarious commands from host 110 and interface with non-volatile memory130 based on these commands. Controller 120 can enable flash memory 130to perform various operations based on control signals received fromhost 110. In examples, this can enable host 110 to program, erase, read,or trim parts of flash memory 130.

In some embodiments, in addition to or instead of an internal volatilememory, controller 120 can interface with an external volatile memory.For example, controller 120 can have access to an external DRAM wheredata can be stored before being transferred to a non-volatile memory.

FIG. 2 is a simplified illustration of the organization of an exampleflash memory 130, according to embodiments. It is to be noted that thestructure shown in FIG. 2 is for illustrative purposes only and theactual physical organization of the flash memory can differsubstantially from the depiction.

In the example shown in FIG. 2, flash memory die 200 comprises twoplanes 210 and 210′. Other examples can include a different number ofplanes per die. A plurality of such dies can be included in a flashmemory, such as flash memory 130. Plane 210 can comprise a plurality ofblocks, such as block 220. Plane 210′ can include a plurality of blocks,such as block 220′. Block 220 can further comprise a plurality of pages230. A page, such as page 230, may share a common word-line and canrepresent a minimum programmable unit. A page can also represent theminimum readable unit. A block can represent the smallest erasable unit.

Dies such as flash memory die 200 can be organized using differentchannels. Each channel can have multiple dies attached to it. Forexample, the first block from the first die, the first block from thesecond die, the first block from the third die, and so on, can begrouped together and accessed in parallel, thereby forming a superblock.Pages belonging to the same superblock can be, for example, programmedand read in parallel. Although a superblock may not be physicallygrouped in a unit, logically, a superblock can behave as a block.

In example, flash memory devices, program and erase operations takeplace at a ‘page’ level, while blocks can represent the smallest unitthat can be erased. When data in an existing page has to be updated, theentire block has to be erased before the updated data is reprogrammed.In these flash memory devices, the system can reserve a certain numberof free blocks to be used when an update request, i.e., a new programrequest, is received.

When the flash memory receives a new program request to update data in apage, the updated data is stored in an empty page, and the old page ismarked invalid or stale. This process can continue until the number offree blocks in the flash memory falls below a certain threshold numberor percentage. When the number or percentage of free blocks falls belowthe threshold, a ‘garbage collection’ procedure can be triggered. In thegarbage collection procedure, valid data of programmed blocks (victimblocks′) can be copied to free ‘target’ blocks, and the victim blockscan be marked as containing invalid data. All data in the invalid blockscan be erased at some point in time to increase the number of freeblocks.

As explained above, this garbage collection process can include a stepof copying data from a first set of locations (e.g., victim block) to asecond set of locations (e.g., target block). Three example locations ofvictim blocks and target blocks are provided in FIGS. 3A-3C.

In FIG. 3A, one example of a victim block and target block is shown.Both the victim block 320 and the target block 322 are located in thesame plane 310 and on the same die 300. In some examples, when methodsfrom embodiments described below are applied to a case where the victimblock and target block are on the same plane, latency of the copyingprocess is lowest.

In FIG. 3B, another example of a victim block and target block is shown.Both the victim block 320 and the target block 322′ are located on thesame die 300; however, target block 322′ is located on a different plane310′ from victim block 320, which is located in plane 310.

In FIG. 3C, another example of a victim block and target block is shown.Victim block 320 and target block 352′ are located on different dies.Victim block 320 is located on die 300, whereas target block 352′ islocated in die 350. Existing commands may or may not support copyingfrom one die to another.

FIG. 4 is a simplified block diagram illustrating a flash memory device400 according to some embodiments. As shown in FIG. 4, flash memorydevice 400 includes a flash memory 410. In some embodiments, flashmemory 410 can be a NAND flash memory, i.e., one based on NAND flasharchitecture such as the architecture described in FIG. 2. Flash memory410 can include a first set of locations 415 and a second set oflocations 420. In some embodiments, data associated with first set oflocations 415 can represent source data to be copied to the second setof locations 420. In some embodiments, data associated with first set oflocations 415 can be copied as-is to the second set of locations 420;whereas in other embodiments, data associated with first set oflocations 415 can be corrected for errors, leading to corrected dataassociated with the first set of locations, before being copied or movedto second set of locations 420.

In some embodiments, first set of locations 415 can be present in avictim block, such as block 320 of FIG. 3; and second set of locations420 can be present in a target block, such as block 322 of FIG. 3.

As shown in FIG. 4, flash memory device 400 can include a flash buffer425. In some embodiments, flash buffer 425 can comprise a page buffer,used to store data related to the corresponding page. For example, thepage buffer in flash buffer 425 can be used to store data read from thepage or data to be written to the page. In some examples, flash buffer425 can comprise other storage area. In some embodiments, when a readcommand is issued by a flash memory controller, flash buffer 425 can beused to store data fetched from flash memory 410. In particular, flashbuffer 425 can be used to store a copy of the data associated with firstset of locations 415. In some embodiments, flash buffer 425 can also beused to store a copy of the data associated with first set of locations415 when an error-fixing operation is performed on the copy of the dataassociated with first set of locations 415.

Flash memory device 400 also includes error-fixing circuitry 430 coupledto flash memory 410. Although not shown in FIG. 4, error-fixingcircuitry 430 can be part of a flash memory circuitry operably coupledto flash memory 410. As shown in FIG. 4, flash buffer 425 anderror-fixing circuitry 430 are included in the flash memory chip 412.

Flash memory device 400 can also include a flash memory controller 450.In examples, flash memory controller 450 can include an Error CorrectionCode (ECC) decoder 455, a controller buffer 460, an ECC encoder 465,controller circuitry 470, a host interface 475, and a flash memoryinterface (not shown in FIG. 4). Such a flash memory interface caninclude elements (e.g., hardware, software, firmware or any combinationthereof) necessary for supporting a flash memory interface protocol.While still forming part of flash memory device 100, in someembodiments, flash memory controller 450 can physically form a separatedevice from flash memory chip 412. In other embodiments, flash memorycontroller 450 can be integrated with flash memory chip 412 to formflash memory device 400.

Data can be obtained from flash memory 410 though the flash memoryinterface and stored in controller buffer 460. ECC decoder 455 can beused to decode and correct errors in the data present in controllerbuffer 460. In certain implementations, flash memory controller 450,using ECC decoder 455, can be used to estimate a count of errors in thecopy of the data associated with first set of locations 415. Examples ofECC can include Hamming codes for SLC NAND flash and Reed-Solomon codesand Bose-Chaudhuri-Hocquenghem codes for MLC NAND flash. In someembodiments, error correction codes can be internally generated. In someembodiments, data in controller buffer 460 can be corrected, encoded byECC encoder 465, and sent to flash memory 410, for example, to be storedin second set of locations 420. However, in other embodiments, othermethods can make ECC correction and re-encoding unnecessary as describedlater in the specification.

Controller circuitry 470 can refer to any processing logic, includingbut not limited to a processor or processing core associated with aprocessor, Application Specific Integrated Circuit (ASIC), FieldProgrammable Gate Array (FPGA), or any other circuitry configurable toexecute instructions. Although not shown in FIG. 4, flash memorycontroller 450 can further comprise a volatile memory such as a DRAM, aDouble Data Rate DRAM (DDR DRAM), or a Static RAM (SRAM). In general,the volatile memory can refer to any memory media where the stored datais lost in the absence of continuous or substantially continuous powersupply.

Host interface 475 can be used to communicate with a host, such as host110 of FIG. 1. Host interface 475 can include elements (e.g., hardware,software, firmware or any combination thereof) necessary for supportinga host interface protocol.

In some implementations, for example, in a garbage collection procedurewhere data needs to be moved from first set of locations 415 in a victimblock to second set of locations 420 in a target bock, flash memorycontroller 450 can issue a command to read the data associated withfirst set of locations 415. Based on such a command, a copy of the dataassociated with first set of locations 415 can be read into flash buffer415. Further, the copy of the data associated with first set oflocations 415 can be read (or ‘fetched’ or copied) to controller buffer460 of flash memory controller 450 (for example, byte by byte). UsingECC decoder 455 and associated circuitry from controller circuitry 470,flash memory controller 450 can decode and correct the errors in thecopy of the data associated with first set of locations 415 present incontroller buffer 460. Corrected data can be encoded and sent byte bybyte by flash memory controller 450 to flash buffer 415 withinstructions from flash memory controller 450 to program the correcteddata to second set of locations 420 in the target block. The correcteddata can be programmed into second set of locations 420 in the targetblock.

This way, data associated with first set of locations 415 can be movedwith error-correction to second set of locations 420, in examples, aspart of garbage collection. The latency of the procedure described abovecan be high because of the time involved in decoding, error correctionby ECC, re-encoding, and/or sending of corrected data from flash memorycontroller 450 to flash buffer 425.

FIG. 5 is a flowchart illustrating a process 500 of moving data in aflash memory from a first set of locations to a second set of locationsaccording to embodiments. One example where process 500 can be appliedis in a garbage collection process in a NAND flash memory. Althoughprocess 500 is explained below as it is performed by flash memory device400 of FIG. 4, it should be noted that other systems and apparatus canbe used in place of flash memory device 400 to perform process 500 andother processes described in the disclosure.

At step 510, process 500 includes reading data associated with the firstset of locations from the flash memory. In some embodiments, step 510can represent a part of, and can be triggered by, the initiation of thegarbage collection process. The garbage collection process itself can betriggered, for example, when the number of available free blocks fallsbelow a certain threshold. For example, when a write command is issuedby a host to a flash memory controller, firmware resident in the flashmemory controller, which tracks the number of free blocks in the flashmemory, can initiate a reclamation of blocks through garbage collection.Garbage collection can include moving valid data from victim blocks totarget blocks, so that victim blocks can then be erased.

In examples, the read command itself can be issued by flash memorycontroller 450. In some embodiments, first set of locations 415, whichcan represent physical addresses corresponding to logical addressesreceived from a host, can be determined by firmware resident on flashmemory controller 450. In some embodiments, a copy of the dataassociated with first set of locations 415 can be made to flash buffer425, and subsequently to controller buffer 460 via a flash memoryinterface on flash memory controller 450.

At step 520, process 500 includes estimating a number of errors in thefirst set of locations. In examples, ECC decoder 455 of flash memorycontroller 450 can decode and estimate or determine error locationsusing an ECC. In implementations, flash memory controller can alsodetermine or estimate the number and addresses of error locations in thedata associated with first set of locations 415. In some embodiments,data is stored in flash memory 410 in binary form, i.e. “1”s and “0”s.

At step 530, process 500 includes determining if the number or errors inthe data associated with the first set of locations is greater than athreshold. In some embodiments, such a determination can be made byflash memory controller 450 using ECC and/or controller circuitry 470.In some embodiments, flash memory controller 450 can make thedetermination of step 530 while operating on a copy of the dataassociated with the first set of locations 415 present in controllerbuffer 460. The copy of the data associated with the first set oflocations 415 present in controller buffer 460 can be the same as thedata associated with the first set of locations 415 because the readinto flash buffer 425 and subsequently into controller buffer 460 can besubstantially error free.

If the number of errors in not greater than a threshold value, at step540, process 500 includes issuing a copy-back command to copy the dataassociated with the first set of locations to the second set oflocations in the flash memory. In some implementations, the thresholdvalue can be calculated accounting for errors already present in thedata associated with the first set of locations (such as from dataretention losses, program-erase cycling, and disturbs) and errors thatcould be introduced from a subsequent programming operation to cause thedata to be stored in the second set of locations. In some embodiments,where process 500 is part of garbage collection, the second set oflocations can be present in a target block. In some embodiments, thecommand to copy the data associated with the first set of locations tothe second set of locations can be issued by flash memory controller450. The data associated with first set of locations 415 can be copiedto second set of locations 420 as-is, without any error correction. Insome embodiments, a command other than a ‘copy back’ command can beused, whereby the data associated with first set of locations 420 iscopied to second set of locations 420 without being routed through flashmemory controller 450. When compared to a method of copying data thatincludes decoding, ECC and encoding at the flash memory controller,process 500 can result in improved latency. This is because flash memorycontroller 450 does not have to re-encode corrected data to a new codeword. Because the number of errors in the data associated with the firstset of locations has been determined to be low, subsequent read of thedata from the second set of locations can be corrected by ECC.

If the number of errors is greater than a threshold value, at step 550,process 500 includes applying ECC and encoding corrected data to resultin corrected, encoded data. At step 560, process 500 includes issuing acommand that causes the encoded corrected data associated with the firstset of locations to be stored in a second set of locations in the flashmemory.

In implementations, using ECC decoder 455 and associated circuitry fromcontroller circuitry 470, flash memory controller 450 can decode andcorrect the errors in the copy of the data associated with first set oflocations 415 present in controller buffer 460. Corrected data can beencoded and sent byte by byte by flash memory controller 450 to flashbuffer 415 with instructions from flash memory controller 450 to programthe corrected data to second set of locations 420 in the target block.The corrected data can be programmed into second set of locations 420 inthe target block.

When the number of errors is low enough to potentially be correctible byECC, process 500 provides the advantage of lower latency by skipping thesteps of the flash memory controller encoding corrected data and sendingit to the flash memory.

FIG. 6 is a flowchart illustrating a process 600 of moving data in aflash memory from a first set of locations to a second set of locationsaccording to embodiments. One example where process 600 can be appliedis in a garbage collection process in a NAND flash memory. Althoughprocess 600 is explained below as it is performed by flash memory device400 of FIG. 4, it should be noted that other systems and apparatus canbe used in place of flash memory device 400 to perform process 600 andother processes described in the disclosure.

At step 610, process 600 includes reading data associated with the firstset of locations from the flash memory. In some embodiments, step 610can represent a part of, and can be triggered by the initiation of thegarbage collection process. The garbage collection process itself can betriggered, for example, when the number of available free blocks fallsbelow a certain threshold. For example, when a write command is issuedby a host to a flash memory controller, firmware resident in the flashmemory controller, which tracks the number of free blocks in the flashmemory, can initiate a reclamation of blocks through garbage collection.Garbage collection can include moving valid data from victim blocks totarget blocks, so that victim blocks can then be erased.

In examples, the read command itself can be issued by flash memorycontroller 450. In some embodiments, first set of locations 415, whichcan represent physical addresses corresponding to logical addressesreceived from a host, can be determined by firmware resident on flashmemory controller 450. In some embodiments, a copy of the dataassociated with first set of locations 415 can be made to flash buffer425, and subsequently to controller buffer 460 via a flash memoryinterface on flash memory controller 450. As explained with reference toFIGS. 3A-3C, in some embodiments, the first set of locations and thesecond set of locations can be on the same plane of the flash memory. Inother embodiments, the first set of locations can be on a first plane ofthe flash memory (FIG. 3A), and the second set of locations can be on asecond plane of the flash memory (FIG. 3B).

At step 620, process 600 includes estimating at least one error in thedata associated with the first set of locations. Although not includedas part of flow 600, in some embodiments, if there are no errors in thedata associated with the first set of locations, a step, such as step540 of FIG. 5, can be used to copy data from the first set of locationsto the second set of locations using a copy back command.

In examples, ECC decoder 455 of flash memory controller 450 can decodeand estimate or determine error locations using an ECC. The estimatingthe at least one error location in the data associated with the firstset of locations can comprise applying an Error Correction Code (ECC)algorithm to the data associated with the first set of locations. Inimplementations, flash memory controller can also determine or estimatethe number and addresses of error locations in the data associated withfirst set of locations 415. In some embodiments, data is stored in flashmemory 410 in binary form, i.e., “1”s and “0”s. In such embodiments,corrected data can be obtained for data in the error locations by bitflipping—i.e., switching ‘0’s to ‘1’s and vice versa.

At step 630, process 600 includes sending information identifying the atleast one error location for error-fixing, the error fixing operating ona copy of the data associated with the first set of locations to resultin corrected data associated with the first set of locations. In someembodiments, flash memory controller 450 can send the informationidentifying the at least one error location for error-fixing based onthe errors and error locations estimated in step 620, for example, byissuing a send command. In such embodiments, the information identifyingthe at least one error location can refer to addresses of the errorlocations, or encoded addresses of the error locations. Becauseinformation identifying the at least one error location is sent to flashbuffer 425 in step 630 as opposed to the entire corrected encoded data,the total size of information sent by flash memory controller 450 ismuch lesser. Hence, latency can also be significantly improved inprocess 600 when compared to processes where corrected and encoded datais sent to the flash memory by the flash memory controller as explainedwith reference to the example below.

When data is stored in the flash memory in binary form, the error-fixingcan comprise a binary flip (changing a 0 to a 1 or a 1 to a 0) of a bitat the one error location in the copy of the data associated with thefirst set of locations.

In some embodiments, the error-fixing can occur at flash buffer 425coupled to the flash memory. In some embodiments, data associated withthe first set of locations can be present in flash buffer 425 from anearlier read operation, such as step 610. In other embodiments, acommand can be issued from flash memory controller 450 to retrieve datafrom the first set of locations to flash buffer 425 in preparation forthe error-fixing. The error-fixing can be performed or assisted bycircuitry and/or logic in error-fixing circuitry 430.

At step 640, process 600 includes issuing a command that causes thecorrected data associated with the first set of locations to be storedin a second set of locations in the flash memory. In some embodiments,the corrected data associated with the first set of locations can bepresent in flash buffer 425. In some embodiments, flash memorycontroller 450 can issue a modified copy back command to cause thecorrected data associated with the first set of locations to be copiedfrom flash buffer 425 to second set of locations 430. The copy backcommand can be modified over an existing copy back command. An existingcopy back command, for example, may be issued to copy data as-is from afirst set of locations in a flash memory to a second set of locationsusing internal circuitry present in flash memory 410. The modified copyback command, on the other hand, can be used to transfer or copy datafrom flash buffer 425 to second set of locations 430.

A summary of the latency saving when the flash memory controller sendsaddresses for error-fixing as opposed to the corrected data is shown inTable 1. In the example shown, the flash page is 16K bytes. For such aflash page, each address, i.e., each error location, can be representedusing 17 bits. In the example in Table 1, the flash interface is assumedto be able to send 200 MBytes per second between flash controller andflash memory. Latency is numerically analyzed and estimated for twosituations: when the entire data is sent, and when error addresses aloneare sent.

TABLE 1 Latency comparison between two schemes: when the entire data issent, and when error addresses alone are sent. Total Data size LatencyTotal Data size Latency (send error (send error (send entire (sendentire address address data scheme) data scheme) scheme) scheme) 0.1%RBER 16*1024*8 = 82 us 17*131 = 1.39 us 131072 bits 2227 (bits) (98.3%decrease) 0.2% RBER 131072 bits 82 us 17*262 = 2.78 us 4454 (bits)(96.6% decrease) 0.5% RBER 131072 bits 82 us 17*656 = 6.96 us 11152(bits) (91.5% decrease) 1.0% RBER 131072 bits 82 us 17*1312 = 13.92 us22304 (bits) (83.0% decrease)

Table 1 illustrates the latency savings when error addresses orlocations alone are sent for different Residual Bit Error Ratespercentages (RBER). For example, in the first row, the RBER is 0.1%.When the entire corrected data associated with the first set oflocations is sent by the flash memory controller to be stored in thesecond set of locations, the total data size is 131072 bits, ascalculated by the size of the page in bits (with 8 bits in a byte). Thisleads to a latency of 82 μs. However, when only error locations aresent, the total data size is 17 times the estimated number of errorlocations (each error location requires 17 bits), which in this case is2227 bits. The latency under this scheme is 1.39 μs, which is a 98.3%improvement. Other examples are provided for different RBER, and all ofthem show marked improvement when only error locations are sent.

Under the scheme where only error locations are sent by the flash memorycontroller, the error-fixing occurring elsewhere (for example, at flashbuffer 425) can introduce some latency. However, the error-fixing, inexamples, comprising of bit flipping, typically comprises simple logic.Hence, the latency introduced by error-fixing using error locationswould be significantly lesser than the latency saved by at least (1)skipping ECC encoding in the flash controller; and (2) sending errorlocations instead of sending all of the data from the flash memorycontroller to the flash memory, leading to a net reduction in latency.

FIG. 7 is a flowchart illustrating a process 700 of moving data in aflash memory from a first set of locations to a second set of locationsaccording to embodiments. One example where process 700 can be appliedis in a garbage collection process in a NAND flash memory. Althoughprocess 700 is explained below as it is performed by flash memory device400 of FIG. 4, it should be noted that other systems and apparatus canbe used in place of flash memory device 400 to perform process 700 andother processes described in the disclosure.

At step 710, process 700 includes reading data associated with the firstset of locations from the flash memory. In some embodiments, step 710can represent a part of, and can be triggered by the initiation of thegarbage collection process. The garbage collection process itself can betriggered, for example, when the number of available free blocks fallsbelow a certain threshold. For example, when a write command is issuedby a host to a flash memory controller, firmware resident in the flashmemory controller, which tracks the number of free blocks in the flashmemory, can initiate a reclamation of blocks through garbage collection.Garbage collection can include moving valid data from victim blocks totarget blocks, so that victim blocks can then be erased.

In examples, the read command itself can be issued by flash memorycontroller 450. In some embodiments, first set of locations 415, whichcan represent physical addresses corresponding to logical addressesreceived from a host, can be determined by firmware resident on flashmemory controller 450. In some embodiments, a copy of the dataassociated with first set of locations 415 can be made to flash buffer425, and subsequently to controller buffer 460 via a flash memoryinterface on flash memory controller 450. As explained with reference toFIGS. 3A-3C, in some embodiments, the first set of locations and thesecond set of locations can be on the same plane of the flash memory. Inother embodiments, the first set of locations can be on a first plane ofthe flash memory (FIG. 3A), and the second set of locations can be on asecond plane of the flash memory (FIG. 3B).

At step 720, process 700 includes estimating a number of errors in thefirst set of locations. In examples, ECC decoder 455 of flash memorycontroller 450 can decode and estimate or determine error locationsusing an ECC. In implementations, flash memory controller can alsodetermine or estimate the number and addresses of error locations in thedata associated with first set of locations 415. In some embodiments,data is stored in flash memory 410 in binary form, i.e., “1”s and “0”s.

At step 730, process 700 includes determining if the number or errors inthe data associated with the first set of locations is greater than athreshold. In some embodiments, such a determination can be made byflash memory controller 450 using ECC and/or controller circuitry 470.In some embodiments, flash memory controller 450 can make thedetermination of step 530 while operating on a copy of the dataassociated with the first set of locations 415 present in controllerbuffer 460. The copy of the data associated with the first set oflocations 415 present in controller buffer 460 can be the same as thedata associated with the first set of locations 415 because the readinto flash buffer 425 and subsequently into controller buffer 460 can besubstantially error free.

If the number of errors is not greater than a threshold value, at step740, process 700 includes issuing a copy-back command to copy the dataassociated with the first set of locations to the second set oflocations in the flash memory. In some implementations, the thresholdvalue can be calculated accounting for errors already present in thedata associated with the first set of locations (such as from dataretention losses, program-erase cycling, and disturbs) and errors thatcould be introduced from a subsequent programming operation to cause thedata to be stored in the second set of locations. In some embodiments,where process 700 is part of garbage collection, the second set oflocations can be present in a target block. In some embodiments, thecommand to copy the data associated with the first set of locations tothe second set of locations can be issued by flash memory controller450. The data associated with first set of locations 415 can be copiedto second set of locations 420 as-is, without any error correction. Insome embodiments, a command other that a ‘copy back’ command can beused, whereby the data associated with first set of locations 420 iscopied to second set of locations 420 without being routed through flashmemory controller 450.

At step 750, process 700 includes estimating at least one error in thedata associated with the first set of locations.

In examples, ECC decoder 455 of flash memory controller 450 can decodeand estimate or determine error locations using an ECC. The estimatingthe at least one error location in the data associated with the firstset of locations can comprise applying an Error Correction Code (ECC)algorithm to the data associated with the first set of locations. Inimplementations, flash memory controller can also determine or estimatethe number and addresses of error locations in the data associated withfirst set of locations 415. In some embodiments, data is stored in flashmemory 410 in binary form, i.e., “1”s and “0”s. In such embodiments,corrected data can be obtained for data in the error locations by bitflipping—i.e., switching ‘0’s to ‘1’s and vice versa.

At step 760, process 700 includes sending information identifying the atleast one error location for error-fixing, the error fixing operating ona copy of the data associated with the first set of locations to resultin corrected data associated with the first set of locations. In someembodiments, flash memory controller 450 can send the informationidentifying the at least one error location for error-fixing based onthe errors and error locations estimated in step 750, for example, byissuing a send command. In some embodiments, because informationidentifying the at least one error location is sent to flash buffer 425in step 760, as opposed to corrected encoded data, the total size ofinformation sent by flash memory controller 450 is much lesser. Hence,latency can also be significantly improved in process 700 when comparedto processes where corrected and encoded data is sent to the flashmemory by the flash memory controller. An illustration of the latencysavings were provided above with reference to Table 1.

When data is stored in the flash memory in binary form, the error-fixingcan comprise a binary flip (changing a 0 to a 1 or a 1 to a 0) of a bitat the one error location in the copy of the data associated with thefirst set of locations.

In some embodiments, the error-fixing can occur at flash buffer 425coupled to the flash memory. In some embodiments, data associated withthe first set of locations can be present in flash buffer 425 from anearlier read operation, such as step 610. In other embodiments, acommand can be issued from flash memory controller 450 to retrieve datafrom the first set of locations to flash buffer 425 in preparation forthe error-fixing. The error-fixing can be performed or assisted bycircuitry and/or logic in error-fixing circuitry 430.

At step 640, process 600 includes issuing a command that causes thecorrected data associated with the first set of locations to be storedin a second set of locations in the flash memory. In some embodiments,the corrected data associated with the first set of locations can bepresent in flash buffer 425. In some embodiments, flash memorycontroller 450 can issue a modified copy back command to cause thecorrected data associated with the first set of locations to be copiedfrom flash buffer 425 to second set of locations 430. The copy backcommand can be modified over an existing copy back command. An existingcopy back command, for example, may be issued to copy data as-is from afirst set of locations in a flash memory to a second set of locationsusing internal circuitry present in flash memory 410. The modified copyback command, on the other hand, can be used to transfer or copy datafrom flash buffer 425 to second set of locations 430.

FIG. 8 illustrates an example computing device 800 comprisingembodiments of the invention. Hardware elements of device 800 can beelectrically coupled via a bus (or may otherwise be in communication, asappropriate). As shown in FIG. 8, computing device 800 includesprocessing unit 804, flash memory device 802, an input/output (I/O)system 810, network circuitry 812, and multimedia circuitry 814. In theexample depicted, processing unit 804 can act as a host system.

In examples, flash memory device 802 can be a NAND flash memory devicesuch as flash memory device 400 of FIG. 4, and can be used to storesecondary data accessed by processing unit 804. Flash memory device 802can include a flash memory controller (not shown) according toembodiments described above, acting as an interface between non-volatilememory device 802 and the processing unit 804. System memory 806 can bea volatile memory such as a Random Access Memory (RAM) and can operatein conjunction with processor 808. Processor 808 can include, withoutlimitation, one or more general-purpose processors and/or one or morespecial-purpose processors (such as digital signal processing chips,graphics acceleration processors, and/or the like)

Computing device 800 can further include network circuitry 812 toconnect computing device 800 to a network. The network circuitry caninclude without limitation a modem, a network card (wireless or wired),an infrared communication device, a wireless communication device and/orchipset (such as a Bluetooth™ device, an 1602.11 device, a WiFi device,a WiMax device, cellular communication facilities, etc.), and/or thelike. Network circuitry 812 may permit data to be exchanged with anetwork, other devices, and/or any other devices described herein.

As shown in FIG. 8, computing device 800 can include multimediacircuitry 814. Multimedia circuitry 814 can connect computing device 800to several external audio and video input and output, such as displaysand speakers. I/O system 810 can connect computing device 800 to variousinput devices and mechanisms such as keyboards, mice, touchscreens,cameras, infra-red capture devices, and the like, and output devices andmechanisms such as a printer, a display unit, a haptic feedback device,and/or the like.

Computing device 800 also can comprise software elements, located withinsystem memory 806 or in flash memory 802, including device drivers,executable libraries, and/or other code, such as one or more applicationprograms, which may comprise computer programs provided by variousembodiments, and/or may be designed to implement methods, and/orconfigure systems, provided by other embodiments, as described herein.Merely by way of example, one or more procedures described with respectto the method(s) discussed above might be implemented as code and/orinstructions executable by a computer (and/or a processor within acomputer); in an aspect, then, such code and/or instructions can be usedto configure and/or adapt a general purpose computer (or other devicesuch as flash memory controller 450 of FIG. 4) to perform one or moreoperations in accordance with the described methods, for example, any ofthe methods illustrated in FIGS. 5-7.

A set of these instructions and/or code might be stored on acomputer-readable storage medium, such as within flash memory device802, or, in examples, within the flash memory controller in flash memorydevice 802. In some cases, the storage medium might be incorporatedwithin a device, such as device 800 or flash memory device 802. In otherembodiments, the storage medium might be separate from a device (e.g., aremovable medium, such as a compact disc), and/or provided in aninstallation package, such that the storage medium can be used toprogram, configure and/or adapt a general purpose computer with theinstructions/code stored thereon. These instructions might take the formof executable code, which is executable by a device and/or might takethe form of source and/or installable code, which, upon compilationand/or installation on a device (e.g., using any of a variety ofgenerally available compilers, installation programs,compression/decompression utilities, etc.) then takes the form ofexecutable code.

Substantial variations may be made in accordance with specificrequirements. For example, customized hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

The terms “machine-readable medium” and “computer-readable medium,” asused herein, refer to any medium that participates in providing datathat causes a machine to operate in a specific fashion. Whileillustrative embodiments of the application have been described indetail herein, it is to be understood that the inventive concepts may beotherwise variously embodied and employed, and that the appended claimsare intended to be construed to include such variations, except aslimited by the prior art.

What is claimed is:
 1. A method for moving data in a flash memory,comprising: reading, by a flash memory controller, data associated witha first set of locations from the flash memory; determining, using anerror-correction code (ECC) decoder at the flash memory controller, atleast one error location in the data associated with the first set oflocations; sending, from the flash memory controller, informationidentifying the at least one error location for error-fixing, theerror-fixing operating on a copy of the data associated with the firstset of locations to result in corrected data associated with the firstset of locations, wherein the error-fixing comprises a binary flip of anerror bit at the at least one error location in the copy of the dataassociated with the first set of locations without copying correcteddata based on ECC encoding from the flash memory controller to the flashmemory; and issuing, from the flash memory controller, a command thatcauses the corrected data associated with the first set of locations tobe stored in a second set of locations of the flash memory, the secondset of locations different from the first set of locations.
 2. Themethod of claim 1, further comprising: determining, at the flash memorycontroller, that a condition is satisfied based on a count of locationswith errors in the first set of locations, and wherein the sending theinformation identifying the at least one error location is based on thecondition being satisfied.
 3. The method of claim 2, wherein thecondition is based on a threshold number of locations with errors in thefirst set of locations.
 4. The method of claim 2, wherein the conditionis based on a threshold percentage of locations with errors in the firstset of locations.
 5. The method of claim 1, wherein the determining theat least one error location in the data associated with the first set oflocations comprises applying an Error Correction Code (ECC) algorithm tothe data associated with the first set of locations.
 6. The method ofclaim 1, wherein the moving data in the flash memory occurs as part of agarbage collection process in a NAND flash memory device.
 7. The methodof claim 1, wherein the error-fixing occurs at a flash buffer coupled tothe flash memory.
 8. The method of claim 1, wherein the command thatcauses the corrected data associated with the first set of locations tobe stored in a second set of locations comprises a modified copy backcommand.
 9. The method of claim 1, wherein the first set of locationsand the second set of locations are on a same plane of the flash memory.10. The method of claim 1, wherein the first set of locations is on afirst plane of the flash memory, and the second set of locations is on asecond plane of the flash memory.
 11. A flash memory device configuredto move data associated with a first set of locations to a second set oflocations, comprising: a flash memory; a flash buffer coupled to theflash memory; a flash memory controller configured to: cause the dataassociated with the first set of locations from the flash memory to becopied to the flash buffer; read the data associated with the first setof locations into the flash memory controller; determine, using anerror-correction code (ECC) decoder, at least one error location in thedata associated with the first set of locations; issue a command thatcauses a corrected data associated with the first set of locations to bestored in the second set of locations, the second set of locationsdifferent from the first set of locations; and error-fixing circuitrycoupled to the flash buffer and configured to: receive the informationidentifying the at least one error location for error-fixing; and issuea correction command to correct the copy of the data associated with thefirst set of locations in the flash buffer based on the informationidentifying the at least one error location to produce the correcteddata associated with the first set of locations, wherein the correctingthe copy of the data associated with the first set of locations in theflash buffer based on the information identifying the at least one errorlocation includes performing a binary flip of an error bit at the atleast one error location in the copy of the data associated with thefirst set of locations in the flash buffer without copying correcteddata based on ECC encoding from the flash memory controller to the flashmemory.
 12. The flash memory device of claim 11 wherein the flash memorycontroller is further configured to: determine that a condition issatisfied based on a count of locations with errors in the first set oflocations, and wherein the sending the information identifying the atleast one error location is based on the condition being satisfied. 13.The flash memory device of claim 12, wherein the condition is based on athreshold number of locations with errors in the first set of locations.14. The method of claim 12, wherein the condition is based on athreshold percentage of locations with errors in the first set oflocations.
 15. The flash memory device of claim 11, wherein the commandthat causes a corrected data associated with the first set of locationsto be stored in the second set of locations comprises a modified copyback command.
 16. The flash memory device of claim 11, wherein the moveof data from the first set of locations to the second set of locationsoccurs as part of a garbage collection process, and the flash memorydevice is a NAND flash memory device.
 17. The flash memory device ofclaim 11, wherein the first set of locations and the second set oflocations are on a plane of the flash memory.
 18. The flash memorydevice of claim 11, wherein the first set of locations is on a firstplane of the flash memory, and the second set of locations is on asecond plane of the flash memory.
 19. A non-transitory computer-readablemedium having stored thereon instructions that when executed by aprocessor perform a method, including: causing data associated with afirst set of locations from a flash memory device to be copied to aflash buffer; reading the data associated with the first set oflocations into a flash memory controller; determining, using anerror-correction code (ECC) decoder, at least one error location in thedata associated with the first set of locations; sending informationidentifying the at least one error location for error-fixing, theerror-fixing operating on a copy of the data associated with the firstset of locations to result in corrected data associated with the firstset of locations, wherein the error-fixing comprises a binary flip of anerror bit at the at least one error location in the copy of the dataassociated with the first set of locations without copying correcteddata based on ECC encoding from the flash memory controller to the flashmemory; and issuing a command that causes the corrected data associatedwith the first set of locations to be stored in a second set oflocations, the second set of locations different from the first set oflocations.